Transverse-Direction, Elastomeric, Breathable Film

ABSTRACT

The present invention provides a multilayer film preferably comprising two skin layers, each preferably comprising low density polyethylene, two outer core layers, preferably comprising an additive and a styrene block copolymer, and an inner core layer preferably comprising an additive and a styrene block copolymer.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/048,408, filed on Feb. 1, 2005, now pending. The disclosure of whichis hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates generally to synthetic films and, morespecifically, to a transverse-direction elastomeric film having amicroporous, breathable structure. The present film preferably has afive-layer structure having generally the following arrangement:skin/outer core/inner core/outer core/skin.

Plastic films are used in a variety of applications. Such films rangefrom single-layer polymers to multilayer structures with various tielayers and copolymers included therein. The use of multiple layersallows for the custom adaptation of a film to meet certain propertyrequirements, ranging from barrier requirements to strengthrequirements.

One use of such films is to provide a barrier layer in diapers,absorbent pads, and the like. In uses wherein the product containing thefilm contacts human skin for a prolonged period of time, such as forexample with diapers, the skin of the person being so contacted islikely to develop a rash or other irritation. Conventional films do notadequately address this problem. What is needed, therefore, is amultilayer film adapted to provide the physical properties desired forfilms used in diapers and the like, while at the same time madebreathable in order to reduce or eliminate rashes and other irritation.

BRIEF SUMMARY OF THE INVENTION

In one embodiment of the present invention the multilayer film of thepresent invention includes a first layer composed of at least onepolyolefin polymer. A second layer is also provided, including at leastone polymer compound, which may be a polyolefin polymer, an ethylenecopolymer resin, a styrene block copolymer, a fluoropolymer,polyvinylchloride, or any other suitable polymer or mixtures thereof.

In one alternative embodiment of the present invention, the second layerof the multilayer film includes a metallocene-catalyzed polymer. Inanother embodiment of the present invention, the second layer furtherincludes an additive, such as calcium carbonate or other suitableadditive.

In a preferred embodiment, the film of the present invention has fivelayers, including two skin layers preferably comprising low densitypolyethylene, two outer core layers, preferably comprising and additiveand a styrene block copolymer, and an inner core layer, preferablycomprising an additive and a styrene block copolymer.

In a preferred embodiment of the invention, the skin layers furtherinclude at least one additive, such as an antioxidant or antiblockingagent. Further, the outer core layers preferably include ametallocene-catalyzed polymer such as metallocene-catalyzed linear lowdensity polyethylene. The additive in the inner and outer core layers ispreferably calcium carbonate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a five-layer film constructed inaccordance with the teachings of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The multilayer film of the present invention has a structure thatincludes at least one first layer of at least one polyolefin polymer,and at least one second layer which includes at least one compoundselected from metallocene-catalyzed polyolefin polymers, ethylenecopolymer resins, styrene-ethylene/butylene-styrene block copolymers,and mixtures thereof. The total thickness of the film may vary dependingupon the intended application of the film. The preferred film has athickness of from about 1.25 mils to about 1.5 mils and, morepreferably, of about 1.34 mils (about 30 g/m²). The thickness ofindividual layers is preferably from about 0.025 mils to about 0.75mils, and more preferably about 0.60 mils.

Turning now to FIG. 1, a preferred embodiment of the present inventionhas five layers in the following configuration: skin layer/outercore/inner core/outer core/skin layer. In the figure, the skin layersare represented by the letter ‘B,’ the outer core layers are representedby the letter ‘A,’ and the inner core layer is represented by the letter‘C.’ In this embodiment of the present invention, it is preferred thateach skin layer comprise about 1%-2% by weight of the total film, or,preferably about 1%-1.5% by weight of the total film or more preferably,comprise about 1% by weight of the total film. It is also preferred, inthis embodiment, that each outer core layer comprise about 18%-24%, byweight, of the total film, or preferably about 20%-24% by weight of thetotal film, or more preferably about 24% by weight of the total film.Finally, in this embodiment it is preferred that the inner core compriseabout 48%-60% by weight of the total film, or preferably about 48%-54%by weight of the total film, or more preferably about 48% by weight ofthe total film. It will be appreciated by those skilled in the art,however, that the thickness of each individual layer may vary from thepreferred thicknesses given above.

The multilayer film of the present invention may be produced byconventional methods used in producing multilayer films, includingcoextrusion and extrusion lamination techniques. For example, the filmmay be formed by coextrusion. Using this method, melted and plasticizedstreams of individual layer materials are fed into a coextrusion die.While in the die, the layers are juxtaposed and combined, after whichthey emerge from the die in a single multilayer film of polymericmaterial. Suitable coextrusion techniques are fully described in U.S.Pat. Nos. 5,139,878 and 4,677,017, incorporated herein by reference tothe extent permitted by law. Coextrusion of the present film may beconducted at temperatures of from about 400° F. to about 510° F.Coextrusion techniques include the use of a feed block with a standarddie, a multi-manifold die, such as a circular die, as well as amulti-manifold die such as used in forming flat cast films and castsheets. The multilayer films of the present invention may also be madeby blown film coextrusion. The film is formed using a blown filmapparatus composed of a multi-manifold circular die head havingconcentric circular orifices. The multilayer film is formed bycoextruding a molten layer through a circular die, and a molten layer onthe other or each opposite side of the first layer through additionalcircular dies concentric with the first circular die. Next, a gas,typically air, is blown through a jet that is concentric with thecircular dies, thereby forming a bubble that expands the individuallayers. The bubble is collapsed onto itself to form a pair of multilayerfilms attached at two opposite edges. Usually, the pair of attachedmultilayer films are then cut apart at one or more of the edges andseparated into a pair of multilayer films that can be rolled up. It ispreferred that the films of the present invention are geared from a flatcast process. An example of the preferred process is provided below.

EXAMPLE 1 Method of Producing Films of the Present Invention

A preferred method for producing the films of the present invention isnow described. As a first step, components are blended at aloss-in-weight blender and combined in the desired proportions(described more fully with respect to specific films, below), then sentto the feed portion of an extruder. This process allows for dry-blendingof ingredients, thereby avoiding the need to utilize more expensive,fully compounded blends. Dedicated extruders mix, melt, and meter thecomponents to a specific film layer. A feed block and flow plate channelthree melt streams into a five layer configuration. The three meltstreams are A) the outer core; B) the skin; and C) the inner core. Thefive layer configuration of the melt streams is as follows: B-A-C-A-B. Aflat, single slot die extrudes the film onto a smooth chill cast roll,producing the flat film product. Next, a series of pre-heat, draw, andannealing rolls provide the film with sufficient machine-directionorientation to induce the formation of micro voids in the structure.These pores allow for water vapor transmission, but are too small toallow passage of liquid. The process of machine-direction orientationalso results in minimal forces required for transverse-directionelongation. The choice of elastomeric material helps ensure adequatestretch and recovery, and conformance to stated physical propertyrequirements. Machine-direction relaxation follows, to minimize filmshrinkage in subsequent, downstream operations. The film is allowed toretract 10%-25% prior to winding.

In the preferred film, the outer skin layers each comprise about 1%-2%by weight of the total film, and are preferably comprised of at leastone polyolefin polymer. Preferred polyolefin polymers includepolyethylene, polypropylene, polybutenes, polyisoprenes, copolymersthereof, terpolymers thereof, α-olefin propylene copolymers, andmixtures thereof. Any other suitable polyolefin polymers may be used.Suitable polyethylenes include, in particular, low density polyethylene(LDPE), linear low density polyethylene (LLDPE), and ultra low densitypolyethylene (ULDPE). Particularly preferred is “barefoot” grade LDPE.Preferred propylene polymers generally have a melting point of 180° C.or above. Preferred propylene polymers further generally have a meltflow index of from about 0.5 g/10 min to about 10 g/10 min at 230° C.,and a force of about 21.6N. Isotactic propylene homopolymer having ann-heptane-soluble content of from about 1-15% by weight, copolymers ofpropylene with C₄-C₈ α-olefins having an α-olefin content of 10% byweight or less, and terpolymers of propylene, ethylene, and butylenehaving an ethylene content of 10% by weight or less and a butylenecontent of 15% by weight or less are preferred propylene polymers. Alsosuitable is a mixture of propylene homopolymers, copolymers,terpolymers, and other polyolefins. The skin layers serve, among otherfunctions, to protect from die buildup, and to minimize or prevent filmblocking or sticking. The skin layers may further include additives suchas antioxidants or antiblocking agents.

In the preferred film, the outer core layers each comprise about18%-24%, and preferably about 24%, by weight of the film as a whole.Each outer core layer preferably comprises about 67% by weight of aneutralizer, such as CaCO₃ (preferably provided in the form of a calciumcarbonate super concentrate, described below), about 26% by weight of astyrene-ethylene/butylene-styrene (SEBS) polymer, such as, for example,Kraton 1657 available from Kraton Polymers (Houston, Tex.), and about 7%by weight of a metallocene-catalyzed polyolefin polymer, such as, forexample, the ethylene α-olefin resin Dow PL 1280, available from DowChemical Company (Midland, Mich.). Other suitable elastomers may be usedin place of the SEBS polymer described above, such as Kraton 6571 andKraton 6936. Likewise, other suitable metallocene-catalyzed polymers maybe used in place of the metallocene-catalyzed polyolefin polymersdescribed above. The outer core layers serve, among other functions, toprovide breathability, some elastomeric performance, durability (withmetallocene-catalyzed polymer), and block-resistant qualities.

In the preferred film, the inner core layer comprises approximately48%-60% by weight of the film. The inner core layer preferably comprisesabout 67% by weight of a neutralizer such as CaCO₃ (preferably providedin the form of a calcium carbonate super concentrate, described below),and about 33% by weight of a high SEBS block copolymer, such as, forexample, Kraton G1657. Other suitable compounds, such asstyrene-ethylene/butylenes-styrene thermoplastic elastomers, or highperformance thermoplastic rubbers may also be used. The inner coreserves, among other functions, to provide breathability and elasticperformance to the film.

The calcium carbonate additive in the inner and outer core layers of thepresent invention may be provided in any suitable manner, but ispreferably provided in the form of a calcium carbonate superconcentrate. This super concentrate preferably contains about 75% Omya2SST calcium carbonate with stearic acid coating, about 0.18% B-900antioxidant (available from Ciba Specialty Chemicals, Tarrytown, N.Y.),about 12.41% Dowlex 2517 LLDPE, and about 12.41% Dowlex 2035 LLDPE.

It will be appreciated by those skilled in the art that additives may beadded to one or more layers of the film of the present invention inorder to improve certain characteristics of the particular layer.Preferred additives include color concentrates, neutralizers, processaids, lubricants, stabilizers, hydrocarbon resins, antistatics, andantiblocking agents. A color concentrate may be added to yield a coloredlayer, an opaque layer, or a translucent layer. Preferred colorconcentrates include color formulations, including black, white, andother colors suitable for the film of the present invention. Preferredcolor concentrates include Ampacet® white PE masterbatch, available fromAmpacet Corporation (Tarrytown, N.Y.). The carrier resin of Ampacet®white PE masterbatch is a LLDPE having a melt index of 20 g/10 min and adensity of 0.92 g/cc. This concentrate has a nominal specific gravity of2.06, a melt index of 3-23 g/10 min, and nominally contains 75% ash.Another preferred color concentrate includes Ampacet® white HDPEmasterbatch, the carrier resin of which is a HD/LLDPE having a nominalmelt index of 10 g/10 min and a density of 0.96 g/cc. This concentratehas a nominal specific gravity of 1.54, a melt index of 9-15 g/10 min,and a pigment composed of 50% TiO₂.

Suitable neutralizers include calcium carbonate, as indicated above, andcalcium stearate. Preferred neutralizers have an absolute particle sizeof less than 10 μm and a specific surface area of at least 40 m²/g.Polymeric processing aids may also be used in a layer. Fluoropolymers,fluoropolymer blends, and fluoroelastomers are particularly preferred,but any processing aid known in the art for use in polymer films issuitable. A particularly preferred processing aid is Ampacet® ProcessAid PE masterbatch, having an LLDPE carrier resin with a nominal meltindex of 2 g/10 min and a density of 0.918 g/cc. The concentrate thereinhas a nominal specific gravity of 0.91, a nominal melt index of 1-3 g/10min, and contains 3% ash.

Lubricants that may be used in accordance with the present inventioninclude higher aliphatic acid esters, higher aliphatic acid amides,metal soaps, polydimethylsiloxanes, and waxes. Conventional stabilizingcompounds for polymers of ethylene, propylene, and other α-olefins arepreferably employed in the present invention. In particular, alkalimetal carbonates, alkaline earth metal carbonates, phenolic stabilizers,alkali metal stearates, and alkaline earth metal stearates arepreferentially used as stabilizers for the composition of the presentinvention.

Hydrocarbon resins and, in particular, styrene resins, terpene resins,petroleum resins, and cyclopentadiene resins have been found to besuitable as additives in order to improve desirable physical propertiesof the film. These properties may include water vapor permeability,shrinkage, film rigidity, and optical properties. In particular,adhesive resins are preferred. A particularly preferred adhesive resinis sold under the trademark Bynel® by DuPont Corporation and isprimarily composed of maleic anhydride modified polyolefin with someresidual maleic anhydride and may also contain small amounts ofstabilizers, additives and pigments.

Preferred antistatics include substantially straight-chain and saturatedaliphatic, tertiary amines containing an aliphatic radical having 10-20carbon atoms that are substituted by ω-hydroxy-(C₁-C₄)-alkyl groups, andN,N-bis-(2-hydroxyethyl)alkylamines having 10-20 carbon atoms in thealkyl group. Other suitable antistatics include ethoxylated orpropoxylated polydiorganosiloxanes such as polydialkysiloxanes andpolyalkylphenylsiloxanes, and alkali metal alkanesulfonates.

Preferred antiblocking agents include organic polymers such aspolyamides, polycarbonates, and polyesters. Other preferred agentsinclude calcium carbonate, aluminum silicate, magnesium silicate,calcium phosphate, silicon dioxide, and diatomaceous earth.

In the preferred embodiments of the film of the present inventiondescribed hereinabove, the film structure is a five-layer structure. Thefive-layer construction allows the highest content of elastomer to beburied inside the inner core layer. This permits other components tofunction as a protective outer core layers to minimize or prevent layersof film from sticking or blocking by minimizing the content of tacky,sticky elastomer in the outer core, and also permits the use ofmetallocene-catalyzed polyolefin polymer in outer core layers in orderto encapsulate the inner core and provide film toughness. Finally, thefive-layer configuration permits the use of a thin, protective LDPEouter skin to provide protection from die build up during the filmcasting process. Because of these advantages, the five-layer embodimentof the present film described above it preferred. It will, however, beappreciated by those skilled in the art upon reading this disclosurethat an alternate number of layers could also be used.

The present invention is further illustrated by the following examples,which are not to be construed in any way as imposing limitations uponthe scope thereof. On the contrary, it is to be clearly understood thatvarious other embodiments, modifications, and equivalents which, afterreading the description herein, may suggest themselves to those skilledin the art, may be used without departing from the spirit of the presentinvention and/or the scope of the appended claims.

Examples of Film Structures in Accordance with the Present Invention

A five-layer film having a total thichness of about 1.5 mils wasproduced using the formula set forth in Table 1. TABLE 1 Formulation A -5 Layer Formulation Percent (w) Layer of Film Polymer AdditiveMetallocene 1 (skin) 1% LDPE 0 0 2 (outer core) 18% 23% SEBS 67% CaCO₃7% ethylene α- olefin resin 3 (inner core) 62% 33% SEBS 67% CaCO₃ 0 4(outer core) 18% 23% SEBS 67% CaCO₃ 7% ethylene α- olefin resin 5 (skin)1% LDPE 0 0

The specific products used in the manufacture of Table 1 film areprovided in Table 2, below. TABLE 2 Formulation B - 5 Layer FormulationPercent (w) Layer of Film Polymer Additive Metallocene 1 (skin) 1% LDPE0 0 2 (outer core) 18% 23% Kraton 67% CaCO₃ 7% Dow 1657 PL1280 3 (innercore) 62% 33% Kraton 67% CaCO₃ 0 G1657 4 (outer core) 18% 23% Kraton 67%CaCO₃ 7% Dow 1657 PL1280 5 (skin) 1% LDPE 0 0

The films described in tables 1 and 2 were produced by the followingprocess. The film was produced by a coextrusion method, with LDPEpresent in the skin layer extruder such that a 1% LDPE skin layer wasproduced on either side of the film. Casting began at a chill roll speedof about 50 meters/minute (about 150 feet/min), with the chill rollspeed being gradually increased to a speed of up to about 75 meters/min(225 f/min). Unstretched film thickness was calculated to be about 3.4mils. MDO temperature was adjusted to 130° F. in preheat, 125-130° F. instretch zones, and 170-175° F. in the final two rolls in the MDO inorder to anneal the film. A stretch ratio of about 3.85× to about 4× wasused to observe film stretching and check film properties. The film wasretracted approximately 18% in the MDO.

A five-layer film having a total film thickness of about 1.50 mils wasproduced using the formula set forth in Table 3. TABLE 3 Formulation C -5 Layer Formulation Percent (w) Layer of Film Polymer AdditiveMetallocene 1 (skin) 1% LDPE 0 0 2 (outer core) 18% 23% Kraton 67% CaCO₃7% Dow 1657 PL1280 3 (inner core) 62% 33% Kraton 67% CaCO₃ 0 Blend (20%1657 + 80% other SEBS thermoplastic elastomer) 4 (outer core) 18% 23%Kraton 67% CaCO₃ 7% Dow 1657 PL1280 5 (skin) 1% LDPE 0 0

A five-layer film having a total film thickness of about 1.5 mils wasproduced using the formula set forth in Table 4. TABLE 4 Formulation D -5 Layer Formulation Percent (w) Layer of Film Polymer AdditiveMetallocene 1 (skin) 1% LDPE 0 0 2 (outer core) 18% 23% Kraton 67% CaCO₃7% Dow 1657 PL1280 3 (inner core) 62% 33% Kraton 67% CaCO₃ 0 Blend (40%1657 + 60% other SEBS thermoplastic elastomer) 4 (outer core) 18% 23%Kraton 67% CaCO₃ 7% Dow 1657 PL1280 5 (skin) 1% LDPE 0 0

The film was tested for elastic performance and breathability. Forelasticity, a two cycle test was used to determine load loss and percentset. The two cycle test was done up to 70% elongation. The sample sizewas three inches in the machine direction by six inches in thetransverse direction. The grip size was three inches in width. The gripseparation was four inches. The samples were loaded such that thetransverse direction of the sample was in the vertical direction. Thepreload was of approximately 10-15 grams set. During the test, the filmwas pulled at 20 inches/min (500 mm/min) to 70 percent elongation (2.8inches in addition to the 4 inch gap), and then immediately returned tothe zero point (the 4 inch gauge separation). The term “percent set”refers to the measure of the amount of the material stretched from itsoriginal length after being cycled. Percent set is defined as the pointat which the retraction curve crossed the elongation axis. The “loadloss” value was calculated as follows:$\frac{{{cycle}\quad 1\quad{extension}} - {{cycle}\quad 2\quad{tension}}}{{cycle}\quad 1\quad{extension}\quad{tension}} \times 100\%$where the extension tension for both cycles is determined at 50%elongation.

The foregoing description of the embodiments of the invention has beenpresented for purposes of illustration and description, and is notintended to be exhaustive or to limit the invention to the precise formdisclosed. The description was selected to best explain the principlesof the invention and practical application of these principles in orderto enable others skilled in the art to best utilize the invention invarious embodiments and with such modifications as are suited to theparticular use contemplated. It is intended that the scope of theinvention not be limited by the specification, but be defined by theclaims as set forth below.

1. A multilayer film comprising: a first skin layer comprising at leastone polyolefin polymer; a first outer core layer comprising an additiveand further comprising a metallocene-catalyzed polymer and at least oneelastomer; an inner core layer comprising an additive and furthercomprising at least one elastomer; a second outer core layer comprisingan additive and further comprising a metallocene-catalyzed polymer andat least one elastomer; and a second skin layer comprising at least onepolyolefin polymer, wherein said inner core layer is situated betweensaid first and second outer core layers and has a composition thatdiffers from said first and second outer core layers, and wherein saidfirst and second outer core layers are situated between said first andsecond skin layers; and wherein the inner core layer comprises a highercontent of elastomer than either of the first or second outer corelayers.
 2. The multilayer film of claim 1 wherein the at least onepolyolefin polymer in said first and second skin layers includes lowdensity polyethylene.
 3. The multilayer film of claim 1 wherein theadditive in said inner core layer and said first and second outer corelayers includes calcium carbonate.
 4. The multilayer film of claim 1wherein the metallocene-catalyzed polymer in said first and second outercore layers is a metallocene-catalyzed polyolefin polymer.
 5. Themultilayer film of claim 1 wherein the additive in said inner core layerand said first and second outer core layers includes calcium carbonate.6. The multilayer film of claim 1 wherein said first and second skinlayers comprise from about 2% to about 4% by weight of said film.
 7. Themultilayer film of claim 1 wherein said first and second outer corelayers comprise from about 36% to about 48% by weight of said film. 8.The multilayer film of claim 1 wherein said inner core layer comprisesfrom about 48% to about 60% by weight of said film.
 9. The multilayerfilm of claim 1 wherein said first and second skin layers furthercomprise at least one additive selected from the group consisting ofantioxidants and anti-blocking agents.
 10. A multilayer film comprising:a first skin layer comprising low density polyethylene; a first outercore layer comprising calcium carbonate,styrene-ethylene/butylene-styrene elastomer, and metallocene-catalyzedlinear low-density polyethylene; an inner core layer comprising calciumcarbonate and styrene-ethylene/butylene-styrene elastomer, wherein theinner core is free of metallocene-catalyzed polyolefin polymer; a secondouter core layer comprising calcium carbonate,styrene-ethylene/butylene-styrene elastomer, and metallocene-catalyzedlinear low-density polyethylene; and a second skin layer comprising lowdensity polyethylene, wherein said inner core layer is situated betweensaid first and second outer core layers and has a composition thatdiffers from said first and second outer core layers, and wherein saidfirst and second outer core layers are situated between said first andsecond skin layers.
 11. The multilayer film of claim 10 wherein saidfirst and second skin layers further include at least one additiveselected from the group consisting of antioxidants and antiblockingagents.
 12. The multilayer film of claim 10 wherein said first andsecond skin layers each comprise from about 1% to about 2%, by weight,of said film, said first and second outer core layers each comprise fromabout 18% to about 24%, by weight, of said film, and said inner corelayer comprises from about 48% to about 60%, by weight, of said film.13. The multilayer film of claim 10 wherein saidstyrene-ethylene/butylene-styrene elastomer in said inner core layercomprises a triblock copolymer.
 14. The multilayer film of claim 10wherein said styrene-ethylene/butylene-styrene elastomer in said firstand second outer core layers comprises a triblock copolymer.
 15. Themultilayer film of claim 10 wherein the inner core layer comprises ahigher content of elastomer than either of the first or second outercore layers.
 16. A multilayer film comprising: a first skin layercomprising low density polyethylene; a first outer core layer comprisingcalcium carbonate, styrene-ethylene/butylene-styrene elastomer, andmetallocene-catalyzed linear low-density polyethylene; an inner corelayer comprising calcium carbonate and styrene-ethylene/butylene-styreneelastomer; a second outer core layer comprising calcium carbonate,styrene-ethylene/butylene-styrene elastomer, and metallocene-catalyzedlinear low-density polyethylene; and a second skin layer comprising lowdensity polyethylene, wherein said inner core layer is situated betweensaid first and second outer core layers and has a composition thatdiffers from said first and second outer core layers; wherein said firstand second outer core layers are situated between said first and secondskin layers; and wherein the inner core layer comprises a higher contentof elastomer than either of the first or second outer core layers. 17.The multilayer film of claim 16 wherein the inner core is free ofmetallocene-catalyzed polyolefin polymer.
 18. The multilayer film ofclaim 16 wherein said first and second skin layers each comprise fromabout 1% to about 2%, by weight, of said film, said first and secondouter core layers each comprise from about 18% to about 24%, by weight,of said film, and said inner core layer comprises from about 48% toabout 60%, by weight, of said film.
 19. The multilayer film of claim 16wherein said styrene-ethylene/butylene-styrene elastomer in said innercore layer comprises a triblock copolymer.
 20. The multilayer film ofclaim 16 wherein said styrene-ethylene/butylene-styrene styreneelastomer in said first and second outer core layers comprises atriblock copolymer.